1. Field of the Invention
The present invention relates to novel catalysts for the treatment of gases, particularly industrial gaseous effluents containing contaminating amounts of sulfur compounds, to catalytically transform the latter into sulfur dioxide.
This invention especially relates to novel monolithic catalysts for the oxidation of hydrogen sulfide into sulfur dioxide.
2. Description of the Prior Art
Certain industrial effluents, and in particular those emanating from Claus process units and which are also referred to as "tail gases", are known to contain oxidizable polluting compounds of sulfur and sometimes sulfur itself. These must be transformed by oxidation into compounds which can be easily eliminated from such gaseous flowstreams.
The sulfur compounds more particularly present in such effluents are hydrogen sulfide and organic compounds of sulfur, such as carbon disulfide, carbonyl sulfide and/or mercaptans. These effluents can be treated in order to transform the compounds of sulfur into sulfur dioxide (SO.sub.2) and carbon dioxide.
Several processes for oxidizing such sulfur compounds are known to this art. The simplest of these known processes entails burning the effluents at high temperatures.
Alternatively, catalytic processes have also been proposed to this art for oxidizing the sulfur compounds into sulfur dioxide.
Among the proposed catalysts, those based on titanium dioxide would appear to present very good performance characteristics. Compare, e.g., European Patent 39,266, which describes a catalyst including, on the one hand, titanium dioxide, or silica, or zirconium dioxide, or mixtures thereof, or silica-magnesia, or zeolites and, on the other, catalytically active elements selected from among those of Groups Ib, IIb, IIIb, Vb, VIb, VIIb, VIII and Va of the Periodic Table and, in particular, copper, silver, zinc cadmium, yttrium, lanthanides, chromium, molybdenum, tungsten, manganese, iron, cobalt, rhodium, iridium, nickel, palladium, platinum, tin and bismuth.
It is also known to use other oxidation catalysts. Thus, U.S. Pat. No. 4,092,404 describes a vanadium-based oxidation catalyst deposited onto a support such as alumina, silica-alumina, silica-magnesia, zirconium dioxide, zirconium dioxide-silica, titanium dioxide, titanium dioxide-silica, silica-zirconium dioxide-titanium dioxide or mixtures thereof.
European Patent 115,449 describes a hydrogen sulfide oxidation catalyst comprising an alumina support, a catalytically active phase selected from among the oxides of at least one of the following metals: Fe, Cu, Ag, W, Co, Ni Cr, Cd and at least one compound selected from among the rare earth oxides, alkaline earth oxides, zirconium dioxide and silica.
The various aforementioned catalysts are generally used in bed form, constituted by a plurality of particles in a column, such bed being traversed by the flow of the gas to be treated.
Hitherto, the catalyst beds have been constituted by catalyst particles in the form of cylindrical or spherical granules formed by molding or extrusion. However, such catalysts do not have a high initial activity with a short contact time, such that it is necessary to conduct the operation employing contact times equal to or greater than approximately 3 seconds. Thus, sulfur trioxide (SO.sub.3) is formed on exiting the catalytic bed.